1. Field of the Invention
The present invention relates to absorbent creped paper wiping products, particularly to multi-ply towels, and to methods of producing such products. An absorbent wiping product of the present invention is further characterized by a structure having a relatively inextensible central ply with outer plies of highly extensible creped tissue paper intermittently adhered thereto.
Some of the most salient advantages of the present structure over prior art structures include: superior caliper and bulk impression when wet due to the fact that the unadhered areas of the outer plies expand in the Z-direction when the structure becomes wetted; improved wet strength due to the resin reinforcement pattern imprinted on both sides of the central ply; and controlled machine direction to cross-machine direction tensile ratio due to the fact that the reinforcing resin can be applied to the central ply in quantities and patterns designed to meet the desired objectives.
The present invention also has relevance to a paper converting process wherein outer plies of highly creped, cellulosic tissue paper are bonded to a resin-reinforced, relatively inextensible central ply by means of pressure exerted between a pair of synchronously driven, hard-surfaced embossing rolls having mating embossment patterns thereon. Each outer ply is thus bonded by means of the uncured resin to the central ply at mating embossment points on the embossing rolls. After the laminating process has been completed, the resin reinforcing pattern imprinted on each side of the central ply is cured, preferably by the application of thermal energy to the structure, to prevent subsequent delamination in use and to maximize the wet strength of the resin, and hence the wet strength of the absorbent wiping product.
2. DESCRIPTION OF THE PRIOR ART
Multi-ply absorbent wiping products are known to be old in the art. Paper toweling having one or multiple plies has been marketed for many years. The known towels vary in basic physical structural characteristics such as ply construction, basis weight, limpness, stretchability, surface texture and the like. Many such prior art structures, however, lose their strength upon becoming wetted and begin to delaminate and/or disintegrate in use. Increasing the bonding area between the adjacent plies of most prior art multi-layered structures is, however, undesirable due to the fact that the product becomes stiffer, thereby losing its softness and drape, and, depending upon the particular adhesive employed, may become less absorbent.
Another disadvantage of most prior art multi-layered structures is that they tend to lose their bulk upon becoming wetted, thereby detracting from the product's stability and hand. Loss of these desirable features is deemed to be a strong negative factor by most consumers.
Recently issued patents disclosing improved absorbent wiping products points to recognition by the industry of the undesirability of the loss of bulk and strength upon the product's becoming wetted.
U.S. Pat. No. 3,695,985 issued to Brock et al. on Oct. 3, 1972, discloses a high-bulk, laminated product having superior strength, high tear and rupture resistance, and good aesthetics. The structure disclosed by Brock et al. is basically a three-ply product having a central ply comprised of a plurality of substantially continuous filaments of a synthetic polymer, preferably isotactic polypropylene or linear polyethylene. Upper and lower cellulosic paper plies are intermittently bonded to the central ply. The adhesive bond area is preferably between approximately 5 to 50 percent of the total web area. The adhesive employed is printed directly on one side of the central ply, as the open character of its structure allows significant flowthrough to its opposite side. The laminate is formed by bringing the cellulosic outer plies into contact with the adhesively printed, continuous filament web at a squeeze roll. The laminate is passed around a heated drum so that the adhesive sufficiently penetrates the cellulosic layers to assure good laminate strength and yet minimize adhesive strike-through to the outer surfaces of the product. The structure is then preferably passed through a calendar stack to assure good bonding. High bulk is provided by hot embossing the laminate structure to set the continuous filament web into a predetermined three-dimensional pattern. This is accomplished by passing the laminate structure between a set of heated, matched engraved rolls to transform the laminate into a three-dimensional pattern which will be set into the web upon cooling. The resulting laminate structure is characterized, according to the Brock et al. disclosure, by its ability to retain a significant portion of its properties such as its strength and bulk even after it has been saturated or wetted with water, i.e., "the wet thickness is at least about 75% of its dry thickness . . . and generally is 80% or more."
Another example of a multi-layered absorbent wiping product having superior strength and bulk when wetted is disclosed in U.S. Pat. No. 3,650,882 issued to Thomas on Mar. 21, 1972. The Thomas patent discloses a three-ply product in which each layer is comprised of absorbent creped tissue paper. The Thomas structure employs a central ply which is highly elastically extensible, whereas the outer plies are of lesser extensibility. The outer plies are bonded to the central ply in spaced regions to provide unbonded zones between bonds. The adhesive employed in joining the several plies together is sufficiently water-resistant to prevent delamination of the webs when wetted so that the highly creped inner web may expand and fill the unbonded zones, thereby providing superior bulk in the wet product. In a preferred embodiment, the adhesive utilized to secure the several webs together is applied in a very thin film to the embossment points on the innermost surface of each outer ply as the several webs proceed to a nip between a pair of embosser rolls which secure the outer plies to the highly creped central ply. It should be noted that while the aforementioned embosser rolls are preferably rotated in unison, the outer plies will not exactly provide their embossments in opposed relation in the nip, and no attempt is made to control the outermost plies to so provide the embossments in opposition. Because the less extensible outer webs of tissue paper confine the expansion of the central ply largely to the unbonded zones, the highly creped central ply, upon wetting, tends to release its crepe, thereby filling the unbonded zones and tending to bulk the towel.
High-bulk, multi-layered absorbent wiping products having a central ply consisting of an open-mesh, cross-thread fabric and outer plies comprised of cellulosic tissue bonded to each of the opposite faces thereof are also disclosed in U.S. Pat. No. 3,708,383 issued to Thomas et al. on Jan. 2, 1973, and U.S. Pat. No. 3,546,056 issued to Thomas on Dec. 8, 1970. The Thomas et al. patent emphasizes the need for heavy embossing so that a substantial portion of the cellulosic tissue in each of the multi-ply outer layers protrudes through the windows of the open-mesh fabric employed as a central ply. Bonding of the two outermost layers of cellulosic tissue to the open-mesh fabric layer is effected by applying adhesive to both the warp and the fill threads to bond the threads to each other as well as to the outermost tissue layers. The Thomas patent discloses a highstrength wiping product formed by coating the opposite sides of an open-mesh scrim comprised of nylon or a similar material with an adhesive, and then combining the scrim with outer layers of highly creped cellulosic tissue in the absence of substantial pressure to minimize loss of stretch in the outermost plies. The lightly adhered composite web is passed over a series of heated rolls at relatively low tension to bond the scrim to the highly creped outer plies. Because the application of heat causes shrinking of the nylon scrim, bulking of the web in the window areas of the scrim occurs, thereby creating puff zones extending between longitudinally projecting threads.
Still another example of a multi-layered absorbent wiping product is disclosed in U.S. Pat. No. 3,687,797 issued to Wideman on Aug. 29, 1972. According to the disclosure of Wideman, layers of creped cellulosic material are bonded by means of spaced adhhesive patterns to a central elastic layer comprised of foam. By securing each absorbent outer ply to the elastic central ply with spaced adhesive patterns, the central ply, which is under tension when the laminate structure is formed, exerts a compressive force on the paper outer plies in the longitudinal direction when the tension is removed, thereby imparting to the composite product, bulk, compressability, and resiliency in a direction perpendicular to the sheet. The laminate structure is preferably formed by applying a regulated pattern of adhesive to the innermost surfaces of the outer plies and joining the outer plies to the central ply while the central ply is under tension by passing the several layers between the nip of a pair of smooth-surfaced rolls. The resulting product is, according to the disclosure of Wideman, "capable of picking up and retaining many times its own weight of water."
It should thus be apparent that most prior art absorbent wiping products exhibiting satisfactory strength and bulk when wet are relatively expensive due, in some instances, to the use of complex manufacturing processes and, in others, to the use of high cost materials of construction. In addition, prior art structures incorporating foam or fabric-reinforced center plies are often difficult to separate into individual sheets, a feature generally desirable in disposable toweling products.
Applicant, on the other hand, has discovered novel and unobvious means of producing a relatively low-cost, heavyduty, multi-layered absorbent wiping product comprised of cellulosic tissue paper, said absorbent wiping product exhibiting high strength and superior caliper and bulk impression, both wet and dry. Applicant has further discovered that the machine direction to crossmachine direction tensile ratio of product made in accordance with the present invention can readily be adjusted to and accurately maintained at any desired level. In addition, applicant has determined that product made in accordance with the present invention exhibits good drape and absorption characteristics which are generally desirable in a paper towel, and that such product is sufficiently durable, in most applications, to be reusable.